The production of polyurethane foams has become increasingly more important in recent years, especially in view of the tremendous increase in the applications which have been found for these materials. For example, foamed polyurethanes have gained significant status in the fields of insulation, electrical equipment, structural elements of furniture, automobile seats and the like.
As the applications for polyurethane foams increase, so do the requirements which must be adhered to with regard to the properties of such foams. One basic requirement which has become more important is the need for the foams to be flame and fire resistant. As a result, various types of materials, both organic and inorganic, have been utilized to impart flame-retardant properties thereto. Many of the additives which have been tested are those which have been previously found effective in fibers, textiles and other plastics. When such materials are applied to polyurethane foams, however, they are generally not effective in practical concentrations or must be used in conjunction with other additives in order to function effectively.
Examples of types of additives which have been suggested for imparting flame-retardance to polyurethane foams include antimony oxide; nitrogen-phosphorus materials such as ammonium orthophosphate, ammonium polyphosphate etc.; mixtures of antimony trioxide and a vinyl halide resin; and mixtures of nitrogen-containing materials with phosphorus-containing compounds, more specific examples of which are used in conjunction with phosphorus-containing or nitrogen-containing polyols, see U.S. Pat. No. 3,134,742 and 3,681,273. Although these patents teach that the enumerated combinations are effective, the phosphorus-nitrogen compounds alone are said to be ineffective.